In the metals industry today, a hot topic is that of steel vs aluminum. Both materials are readily available, both are recyclable, and both offer corrosion resistance. So what is driving the hype, and the competitive nature of this rivalry?
It first came to my personal attention around 2010 when I was at a traditional carbon steel coil processor, and I saw aluminum being processed for Camaro and Mustang hoods. This was a part of the drive towards lighter weight vehicles for improved fuel mileage under the mandate of the CAFE standards. CAFE standards (Corporate Average Fuel Economy) in a nutshell, are minimum mile-per-gallon requirements set by vehicle class by the government. In the early 2000’s when it became apparent lighter weight materials would be more in demand, the steel industry got very serious about developing lighter gauge, but much higher strength steels. A few other industries followed automotive’s suit and looked at lighter gauge/higher strength steel.
From the November 2017 AIST article by Sam Kusic, “First came the surprise when Ford Motor Co. announced in 2012 that it would make an aluminum-bodied version of its F-150 pickup truck. And then came the panic when the forecasts began to emerge of a major shift in materials choice for North American pickup trucks. One, in fact, predicted that 75% of North American pickups would have an aluminum body by 2025. But a funny thing happened on the way to the automotive steel apocalypse — it never happened. And since the Ford announcement, no other automakers have announced an aluminum-intensive lightweighting strategy for their vehicles, according to Jody Hall, automotive vice president for the Steel Market Development Institute. “But you hear a lot about how automakers are utilizing the latest grades of high-strength steel and advanced high-strength steel (AHSS) to better design their vehicles and achieve the mass reduction they need at the performance they desire,” said Hall. “And we even have seen some companies going back from aluminum to steel,” she said. Jody goes on to say, “Steel remains an attractive material because the combination of its performance — its strength and durability — and cost-effectiveness in terms of mass reduction make it an optimal choice.”
So for Spahr and the manufacturers we supply, what factors should we consider?
Let’s quickly examine both materials.
Steel is made of alloys of iron and carbon. Aluminum’s base is bauxite, which is mined primarily in tropical areas. Bauxite is ground into a paste called alumina, which is then smelted with molten cryolite and induced with electrical shock. The ions separate, and the liquid cools and becomes aluminum.
Cost – Aluminum is much more expensive than carbon steel. Repairing aluminum is also more expensive than repairing steel.
Formability – Aluminum is very malleable and formable but so are steel grades designed for high elongation %, such as FS and DS, DDS and EDDS.
Corrosion Resistance – Aluminum is highly corrosion resistant. As-is, it does not require further treatment (i.e. chem-treats, paint, coatings, etc…). However, carbon steel even when galvanized, chem-treated, and painted is still cheaper than aluminum.
Weight – Aluminum is lighter than steel since it is less dense. However, that difference in density leads us to strength…
Strength – Carbon steel wins. Steel’s carbon content makes it harder, more dent resistant, and more durable when stressed. Steel is strong and less likely to warp, deform or bend under weight, force or heat. For appearance, steel is also less likely to scratch.
The bottom line: A Massachusetts Institute of Technology study with cost models demonstrates aluminum to be significantly more costly than steel – not just initially but overall. Study results show (A) production of aluminum is two to three times more expensive than steel, (B) manufacturing and assembly with aluminum is 20 % to 30 % more expensive than steel, and (C) the mass reduction with steel can be achieved at very low cost, while engineering studies show low-density materials like aluminum cost more in engineering per pound savings in weight.
Where aluminum really shines is in aerospace applications, where lightweight is absolutely essential to facilitate a plane or a rocket to get off the ground. For most manufacturing though, steel is still the go-to metal of choice.